生物产甲烷的生化代谢途径现状及问题

产甲烷生化代谢途径研究进展*

方晓瑜1,2,3李家宝1,4,5芮俊鹏1,4,5李香真1,4,5**

1中国科学院环境与应用微生物重点实验室, 成都生物所, 成都610041

2中国科学院成都生物研究所环境微生物四川省重点实验室, 成都610041

3中国科学院大学, 北京100049

4中国科学院山地生态恢复与生物资源利用重点实验室, 成都生物所, 成都610041

5生态系统恢复与生物多样性保育四川省重点实验室, 成都生物所, 成都610041

摘要微生物产甲烷过程产生的甲烷约占全球甲烷产量的74%。产甲烷过程对生物燃气生产和全球气候变暖等都有重要的意义。本文综述了产甲烷菌的具体生化代谢途径，其本质是产甲烷菌利用细胞内一系列特殊的酶和辅酶将CO2或甲基化合物中的甲基通过一系列的生物化学反应还原成甲烷。在这一过程中，产甲烷菌细胞能够形成钠离子或质子跨膜梯度，驱动细胞膜上的ATP合成酶将ADP转化成ATP以获得能量。根据底物类型的不同，可以将该过程分为三类：还原CO2途径、乙酸途径和甲基营养途径。还原CO2途径是以H2或甲酸作为主要的电子供体还原CO2产生甲烷，其中涉及到一个最新的发现—电子歧化途径；乙酸途径是乙酸被裂解产生甲基基团和羧基基团，随后，羧基基团被氧化产生电子供体H2用于还原甲基基团；甲基营养途径是以简单甲基化合物作为底物，以外界提供的H2或氧化甲基化合物自身产生的还原当量作为电子供体还原甲基化合物中的甲基基团。通过这三种途径产甲烷的过程中，每消耗1mol底物所产生ATP的顺序为还原CO2途径>甲基营养途径>乙酸途径。由于产甲烷菌自身难以分离培养，未来将主要通过现代的生物技术和计算机技术，包括基因工程和代谢模型构建等最新技术来研究产甲烷菌的生化代谢过程以及其与其他菌群之间的相互作用机制，以便将其应用于生产实践。

关键词：产甲烷菌；生化代谢；还原CO2途径；乙酸途径；甲基营养途径

CLC Q939.99

收稿日期Received: 接受日期Accepted:

*国家重点基础研究发展规划资助项目（973项目，2013CB733502）；国家自然科学基金资助项目（31300447，41371268）资助Supported by State Key Basic R & D Program of China (973 Program, No. 2013CB733502 ), the National Natural Science Foundation of China (No. 31300447，41371268).

**通讯作者Corresponding author (E-mail: lixz@)

Biochemical pathways of methanogenesis*

FANG Xiaoyu1,2,3, LI Jiabao1,4,5 RUI Junpeng1,4,5 & LI Xiangzhen1,4,5**,

1Key Laboratory of Environmental and Applied Microbiology, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, 610041, PR China

2Environmental Microbiology Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, 610041, PR China

3University of Chinese Academy of Sciences, Beijing 100049, PR China

4Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China

5 Ecological Restoration Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, PR China

Abstract

Microbial methanogenesis accounts for approximately 74% of natural methane emission. The processes play major roles in global warming and are important for bioenergy production. This paper reviews the biochemical pathways of methanogenesis. It is currently accepted that methanogenesis proceeds via three biochemical pathways depending on the carbon sources, including hydrogenotrophic, aceticlastic, and methylotrophic methanogenesis. Multiple enzymes and coenzymes are involved in the processes, during which Na+ or proton gradient is created across the cell membrane, contributing to limited A TP synthesis. In the hydrogenotrophic pathway, CO2 is reduced to methane with H2 or formate as an electron donor. In the aceticlastic pathway, acetate is split into methyl and carboxyl group, then the carboxyl group is oxidized to produce H2 which is used as the electron donor to reduce methyl group. In the methylotrophic pathway, methyl group is reduced with external H2or reducing equivalent from the oxidation of its own methyl group. The A TP gains per mole substrate for different pathways are as follows: hydrogenotrophic > methylotrophic > aceticlastic pathway. Due to the unculturability of most archaeal methanogens, new technologies, such as bioinformatics, gene engineering and modelling, could be applied to investigate the biochemical pathways of methanogenesis, and the relationship between methanogens and other microbial communities.

Keywords methanogen; methanogenesis; biochemical pathways; CO2-reducing; methylotrophic; aceticlastic methanogenesis

CLC Q939.99